1. Field of the Invention
The present invention relates to an electroconductive member for electrophotography to be used in electrophotographic apparatus such as an electrophotographic copying machine and an electrophotographic printer, and a process cartridge and electrophotographic apparatus using the electroconductive member for electrophotography.
2. Description of the Related Art
An electrophotographic image forming apparatus includes a photosensitive member serving as a member to be charged, a charging device, an exposure device, a developing device, a transfer device, and a fixing device. As the charging device, there has been widely adopted a charging device configured to charge a surface of a photosensitive member by applying a voltage to a charging member that is held in contact with or arranged closely to the surface of the photosensitive member.
In recent years, the electrophotographic image forming apparatus has output more graphic patterns due to the further advancement in colorization, with the result that there is an increasing demand for images with higher definition.
When the electrophotographic image forming apparatus is used to output high-definition images, even minute charging unevenness, which has not become a problem heretofore, may appear as density unevenness on images.
As one of the main causes for the charging unevenness, there is given the adhesion of foreign matter to a surface of the charging member during use. The foreign matter, such as a toner, an external additive, or shaved powder of a photosensitive drum, adheres to the surface of the charging member used in a contact charging method along with use so as to contaminate the surface gradually. When the foreign matter adheres to the surface of the charging member, charging unevenness occurs, with the result that streak-like or spot-like density unevenness may occur on images. Such density unevenness is recognized particularly significantly, on half-tone images. Further, such density unevenness is liable to occur particularly in a DC charging method that involves charging the photosensitive drum by applying only a DC voltage to the charging member.
In order to solve the above-mentioned problem, Japanese Patent Application Laid-Open No. 2000-19814 discloses an electroconductive member capable of being used as a charging roller, which has a minute uneven structure on a surface.